This invention relates to electric motors and more particularly to single phase alternating current induction motors in which the main and auxiliary windings are interchanged to provide for efficient operation at two output power levels.
Certain electric motor applications require that the motor drives a load at various levels of shaft horsepower. For example, dual stroke compressors and gear change compressors which are used in heat pumps operate at variable capacity levels while being driven at essentially constant speed. A characteristic of these compressors is that when running at reduced capacity they require considerably less shaft horsepower than when operating at full capacity. The efficiency of a normally applied permanent split capacitor motor suffers significantly at the reduced load thereby hurting the system performance at reduced capacity. Since systems studies indicate that such a compressor used in a heat pump may operate at about 80% of its hours at reduced capacity, it is desirable to enhance the low capacity efficiency. The present invention provides a motor which operates at two output power levels with an efficiency which is greater than that found in conventional permanent split capacitor motors when operated at similar power levels.